Of course, when I want to read about female killers, I go to:
http://unknownmisandry.blogspot.com/
But Unca Bob has been making some efforts to document the psychology of female killers lately:
http://uncabob.blogspot.com/2015/03/the-psychology-of-female-serial-killers.html
one in six serial killers are female. Their crimes tend to go undetected for longer than their male counterparts, likely in part because “our culture is in denial of women’s proclivity for aggression.”